Process for manufacturing a hollow turbomachine blade and a multiple-action furnace press for use in said process

ABSTRACT

A process for manufacturing a hollow turbomachine blade made from a type TA6V titanium alloy includes a hot forming step in which an element of the blade is isothermally shaped in a press at a temperature between 700° C. and 940° C. under the action of at least two stamps and a holding-clamp which press the blade element on a shaping die, while ensuring a controlled deformation rate so as to obtain a lengthening of the fibers, that is to say the elongation of the different fibers of the element, with a controlled distribution on both sides of the central fiber. A multiple-action furnace-press designed for carrying out the process is also described.

This application is a Division of Ser. No. 08/871,637 filed Jun. 9,1997, U.S. Pat. No. 5,933,951.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the manufacture of ahollow turbomachine blade, particularly a large chord fan rotor blade,and to a multiple-action furnace press for use in the process.

The advantages of using large chord blades in turbomachines areparticularly apparent in the case of the fan rotor blades in bypassturbojet engines. However, such blades must cope with severe conditionsof use and, in particular, must possess satisfactory mechanicalcharacteristics combined with anti-vibration properties and resistanceto impact by foreign bodies. The need to achieve sufficient speeds atthe tips of the blades has also led to seeking a reduction in the massof the blades, and this has been achieved, in particular, by usinghollow blades.

2. Summary of the Prior Art

EP-A-0700738 describes a process for the manufacture of a hollowturbomachine blade, especially a fan rotor blade having a large chord.In a first stage (a) of this process a computer-aided design andmanufacturing (CAD/CAM) system is used to create, starting from ageometric definition of the blade to be obtained, a digital simulationconsisting of computing for the constituent parts of the blade, on bothsides of the central fibre, the lengths of the fibres as a function oftheir position relative to the axis 20 of the respective part 19 asshown in FIG. 1, the parts being flattened. Also carried out at thisstage is a digital simulation of an operation to shape the parts bytwisting, for comparison with the final result.

After this first stage the manufacturing process known from EP-A-0700738involves the following steps:

(b) die-forging the primary parts of the blade in a press.

(c) machining the primary parts;

(d) depositing diffusion barriers on at least one of the parts accordingto a predefined pattern;

(e) assembling the primary parts and diffusion welding them togetherunder isostatic pressure;

(f) inflating the welded assembly using pressurized gas and superplasticshaping the assembly; and,

(g) final machining of the shaped assembly

One of the aims of the invention is to make it possible to perform,during the above sequence of operations, an additional shaping of theparts by twisting, without any risk of causing buckling typecorrugations along the central fibre. These corrugations are generatedby compression stresses induced at the time of the elongation of thelateral fibres resulting from the length differences between the initialflat part and the twisted part.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a process for manufacturing a hollowturbomachine blade of the type which is known from EP-A-0700738, whereinsaid process includes a step of hot forming an element of the blade,which is made of a titanium alloy of TA6V type, in a press at atemperature between 700° C. and 940° C. using the action of at least twostamps and a holding clamp locking said element on a shaping die whileensuring a controlled deformation rate, so as to obtain a lengthening ofthe fibres of said element, that is to say the elongation of differentfibres of said element, with a controlled distribution of said fibres onboth sides of the central fibre.

It is known to carry out hot forming operations using special meansincluding a heating enclosure associated with heating means, a press-bedstructure associated with a power assembly comprising a plurality ofactuators, and forming equipment. However, these known means areinadequate for carrying out the hot forming operation in the process inaccordance with the invention.

Accordingly, the invention also provides a multiple-action furnace-presscomprising: a heating enclosure; heating means associated with saidheating enclosure; a press bed structure surrounding said heatingenclosure and consisting of a lower metal plate, an upper metal plate,and columns inter-connecting said lower metal plate and said upper metalplate, said columns comprising prestressed tie rods; forming equipmentcomprising a lower soleplate incorporating a shaping die bounded at eachend by a respective notch, an upper holding clamp for holding saidelement on said shaping die during deformation, and at least two upperstamps; multiple actuators connected to said holding clamp and saidstamps; and a power unit for driving said multiple actuators.

The use of the multiple-effect furnace-press in accordance with theinvention for the hot forming step in the blade manufacturing processenables the drawbacks of the earlier known processes to be avoided andblades to be obtained possessing improved geometric and mechanicalcharacteristics optimized to the conditions of use, and also enablesrepeat quality to be ensured while facilitating relatively low costmanufacturing conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents diagrammatically the results of a digital simulationof a fibre lengthening operation to be carried out on a constituent partof a hollow blade assembly produced by the process in accordance withthe invention;

FIG. 2 shows a perspective view of the welded assembly of the hollowblade after twisting;

FIG. 3 shows a diagrammatic sectional view of a multiple-actionfurnace-press in accordance with the invention for use in themanufacture of a hollow turbomachine blade;

FIG. 4 shows a diagrammatic transverse sectional view of themultiple-action furnace-press shown in FIG. 3;

FIG. 5 shows a detail of the connection between an actuator and atransmission rod of the furnace-press shown in FIGS. 3 and 4;

FIG. 6 shows a detail similar to that of FIG. 5 of the connectionbetween a transmission rod and the holding clamp or a stamp of thefurnace-press shown in FIGS. 3 and 4;

FIG. 7 shows a diagrammatic perspective view of the holding clamp of thefurnace-press shown in FIGS. 3 and 4;

FIG. 8 shows a diagrammatic view of the placement of the centering pegsof the shaping equipment relative to the furnace-press;

FIG. 9 shows a diagrammatic perspective view of the shaping equipmentarranged inside the furnace-press of FIGS. 3 and 4;

FIG. 10 shows a diagrammatic perspective view of further shapingequipment used for a twisting operation after the fibres have been setto length; and,

FIG. 11 shows a diagrammatic view of a loading and unloading device foruse with the furnace-press of FIGS. 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the manufacture of a hollow turbomachine fan blade by a process inaccordance with the invention, the element which is subjected to a hotforming operation in an intermediate manufacturing stage may be either aforged primary skin intended to constitute either the intrados or theextrados surface of the blade, or a central metal sheet intended to formstiffeners inter-connecting the intrados and extrados surface skins ofthe blade, or a welded assembly including the outer skins and at leastone central metal sheet of the blade, or an unwelded pre-assembled unitincluding the outer skins and at least one central metal sheet of theblade, or a welded assembly including an intrados surface skin and anextrados surface skin. In the following description of a non-limitativeembodiment of the invention the element is a welded assembly 9, shown inFIG. 2 in a stage in the manufacture of a hollow great chord fan bladefor a turbomachine.

A preliminary digital simulation operation is carried out using acomputer-aided design and manufacturing (CAD/CAM) system in a mannerwhich is known, such as from the aforementioned EP-A-O 700 738. Thissimulation aims to maintain the lengths of the fibres on both sides ofthe neutral axis as a function of their position relative to the axis 20of the element 19, as shown in FIG. 1. The control related to thelengthening of the fibres enables the thinning of the welded assembly tobe estimated as a function of the distribution of the elongation ratioof the said fibres. A data processing computation then enablesvariations in thickness of the primary skins to be compensated so as toobtain the desired final thickness after all the stages of themanufacturing process.

On the basis of the elements thus determined, the process formanufacturing a hollow turbomachine blade, which in this example is agreat chord fan rotor blade 9, includes a step of hot forming a weldedassembly 9 made of a titanium alloy of the TA6V type, the hot formingstep consisting of isothermally shaping the welded assembly at atemperature between 700° C. and 940° C. in a press under the action ofat least two stamps and a holding clamp acting on the welded assemblyplaced on a shaping die, while ensuring a controlled deformation rate soas to achieve a lengthening of the fibres of each element of theassembly, i.e. the elongation of the different fibres of each element,with a controlled distribution of these fibres on both sides of thecentral fibre.

Preferably, the operation is carried out by keeping the welded assemblyunder the conditions for superplasticity of the titanium alloy used.Tests conducted on a TA6V type titanium alloy were carried out between880° C. and 940° C., and the corresponding deformation rate was chosento conform to the superplasticity condition, thus making it possible toavoid any trace of localized constriction of an element of the weldedassembly 9.

Depending on the final shape of the blade to be obtained for aparticular application, the operation of lengthening the fibres by hotforming may be preceded by a cambering operation performed on the rootof the blade and in the area of the base of the aerofoil portion of theblade. In other cases, depending on the means used and/or on the resultto be obtained, a single hot forming operation may be effective to carryout the cambering of the root and the base area of the aerofoil portionas well as the lengthening of the fibres.

Also depending on the particular application and the final shape of theblade to be obtained, the operation of lengthening the fibres of thewelded assembly in the hot forming step may be followed by an inflationoperation using pressurized gas and super-plastic shaping to achieve theprofiles required for the blade.

As an alternative, after the fibre lengthening operation, an additionalforming operation comprising twisting and calibration may be necessary.In this case, the twisting operation is preferably carried out after thefibre lengthening operation and without intermediate cooling of thewelded assembly 9.

The multiple-action furnace-press shown in FIGS. 3 and 4 may be used forcarrying out the hot forming operation for lengthening the fibres of thehollow turbomachine blade element 9 in the manufacturing process of theinvention as just described.

This furnace-press comprises two distinct parts: a lower part includinga heating enclosure 47, equipment 21 for lengthening the fibres, and apress bed structure; and an upper part including a power unit having asmany actuators 60 as are necessary depending on the forming operation.The power unit may be connected to the lower part by an arched support61, such as diagrammatically shown in FIG. 4.

The press bed structure is composed of two metal plates 48, 49dimensioned according to the stresses to be generated, connected by fourcolumns 50, each of which comprises a prestressed tie rod 51. Withinthis structure, a furnace 47 which is capable of being heated to atemperature between 700° C. and 940° C. houses the equipment forlengthening the fibres of the element to be shaped, particularly thewelded assembly 9 of the hollow turbomachine blade.

The equipment for lengthening the fibres consists of three distinctparts: a soleplate 21 incorporating the die for lengthening the fibres;a holding clamp 45 for cambering the root and an adjacent part of theblade and for holding the welded assembly 9 during the lengthening ofthe fibres; and at least two stamps 46, there being three in theembodiment shown in the drawings.

In the forming tool shown in FIG. 9, the soleplate 21 is made of arefractory alloy or ceramic material and includes the CAD/CAM produceddie for lengthening the fibres. This die comprises the solid parts ofthe root 62 and the tip 63 of the blade, one or more corrugations23-24-25-26 corresponding to the desired elongations of the element ofFIG. 1, and the pivots 40-41 of the welded assembly 9 of FIG. 2.Moreover, the soleplate includes guide pillars 72 for the positioning ofthe holding clamp 45, and pillars 71 for precisely positioning thewelded assembly on the soleplate before shaping.

The holding clamp 45 shown in FIG. 7 consists of a unitary castingcontaining a number of cells 73 equal to the number of the stamps 46. Italso has two holes 74 to ensure perfect positioning of the holding-clampand of the stamps relative to the soleplate 21 when receiving the guidepillars 72. The central partition 75 formed between the two lateralcells serves to hold the welded assembly 9 along the central axis duringthe shaping operation as shown in FIG. 4. The holding-clamp 45 alsoincludes impressions of the curvilinear or rectilinear root 62 and tip63 of the blade element. The impression 62 also permits cambering of theroot and the adjacent part of the blade element before immobilizing thewelded assembly 9 during the fibre lengthening stage.

The soleplate 21 is fixed or merely set on the floor of the furnace 47.The holding-clamp 45 and the stamps 46 are movable, and are connected tothe power unit by means of transmission rods 54 fitted withT-connections 55 and 59, as shown in detail in FIGS. 5 and 6, in orderto accommodate the differential expansions at the holding-clamp 45 andthe stamps 46, and also at the connections to the ends of the actuators60. These T-connections thus provide a heat barrier between the ends ofthe actuators and the transmission rods. Moreover, the connections 59between the holding-clamp 45 and the transmission rods 54 are able topermit rotation through 90° so as to disconnect the transmission bars 54and permit the insertion and removal of the equipment for lengtheningthe fibres into and out of the heating enclosure or furnace 47.

In order to make the expansions unidirectional and thereby simplify theT-connections, the furnace 47 and the forming equipment 21 arejudiciously positioned relative to the lower part of the press by meansof centering pegs 56, as shown in FIGS. 3 and 4 and the detail of FIG.8. These pegs 56 are positioned according to the arrangement of thestamps 46, generally along the longitudinal axis of the press, andaccording to the number of stamps, as shown diagrammatically in FIG. 8.

The guidance of the transmission rods 54 is ensured by collars 58 madeof a ceramic compound and fitted in the upper metal plate 48 of thelower part of the press. The extent of these collars is sufficientlylong to guide perfectly the group of transmission rods 54 passingthrough the roof of the furnace. Preformed sleeves 57 made of fibrouscompounds and fitted with metal tubes of refractory material serve tocool the transmission rods 54 if the operating cycle is relativelyshort. However, for lengthy operations the transmission rods 54 areprovided with channels for the flow of a cooling fluid.

The press control system provides fine control of the speed of thestamps 46 so as to stay permanently within the superplastic range of thematerial, such as the type TA6V titanium alloy, used for the manufactureof the hollow turbomachine blade, while ensuring a slow rate ofdeformation. The deformation rate is controlled by means of a hydraulicunit 70 which is capable of providing a range of speeds between 50 mms⁻¹ and 0.05 mm s⁻¹.

An example of the use of the press to carry out a forming operation inaccordance with the invention on a welded assembly 9 of a hollowturbomachine blade, will now be described. The heating enclosure 47 israised to a temperature in excess of 880° C. for a forming operation ona TA6V titanium alloy. The holding-clamp 45 and the stamps 46 are in theraised position and provide a space allowing the introduction of thewelded assembly 9 onto the soleplate 21 in the enclosure 47 using aloading device 79 as diagrammatically represented in FIG. 11. The device79 has two clamps 80 for holding the welded assembly 9 by the pivots 40and 41 and applying a longitudinal tractive force to the assembly.

The welded assembly is positioned on the soleplate 21 by means of thepivots 40-41 being vertically guided between the cylindrical pillars 71of the base. At this stage, the welded assembly 9 rests on the soleplate21 until it reaches the forming temperature. As soon as the temperatureis reached, the forming process begins by simultaneously moving theholding-clamp 45 and the stamps 46 down to a predetermined position athigh speed, and then stopping the stamps 46. The downward movement ofthe holding-clamp 45 continues at superplastic forming speed to the endof stroke position, following which the lengthening of the fibres isthen achieved by moving downwards one or more of the stamps 46 eithersimultaneously or individually. As soon as the end of stroke positionhas been reached by the complete set of stamps 46, the holding-clamp andthe stamps are raised to their starting position. The unloading of theformed welded assembly is then effected by means of the device 79 which,thanks to the tractive force applied by the device, prevents buckling ofthe shaped unit 9 under its own weight.

In the case where a twisting and calibrating operation is necessaryafter the forming operation involving lengthening the fibres, the weldedassembly 9 is replaced between two tools of suitable shape at anisothermal temperature which is between 700° C. and 940° C. for a weldedassembly made a titanium alloy of TA6V type. One example of a tool isshown in FIG. 10 and includes a soleplate 65 and a forming die 66bounded at each end by grooves 67 and 68. The welded assembly 9 ispositioned on the tool by means of its pivots 40 and 41 being guidedvertically by cylindrical pillars 69 so as to maintain the central fibredefined by the pivots 40 and 41 in a vertical plane between the pillars69 throughout the deformation.

We claim:
 1. A multiple-action furnace press for the hot forming of anelement for use in the manufacture of a hollow turbomachine blade by aprocess comprising the following steps: using computer aided design andmanufacturing (CAD/CAM) means to create, from a definition of said bladeto be produced, a digital simulation of the flat form of the primaryparts of said blade; die-forging said primary parts of said blade;machining said primary parts; depositing diffusion barriers on at leastone of said primary parts according to a predefined pattern; inflatingthe welded assembly of said primary parts using pressurized gas andsuperplasticly shaping said assembly; and, final machining of saidshaped assembly; wherein said process also includes a step of hotforming an element of said blade by isothermally shaping said element,said element being made of a titanium alloy of TA6V type, in a press ata temperature between 700° C. and 940° C. using the action of at leasttwo stamps and a holding clamp locking said element on a shaping diewhile ensuring a controlled deformation rate, so as to obtain alengthening of the fibres of said element, that is to say the elongationof different fibres of said element, with a controlled distribution ofsaid fibres on both sides of the central fibre, said multiple-actionfurnace press comprising: a heating enclosure; heating means associatedwith said heating enclosure; a press bed structure surrounding saidheating enclosure and consisting of a lower metal plate, an upper metalplate, and columns inter-connecting said lower metal plate and saidupper metal plate, said columns comprising prestressed tie rods; formingequipment comprising a lower soleplate incorporating a shaping diebounded at each end by a respective notch, an upper holding clamp forholding said element on said shaping die during deformation, and atleast two upper stamps; multiple actuators connected to said holdingclamp and said stamps; and a power unit for driving said multipleactuators.
 2. A multiple-action furnace press according to claim 1,wherein said holding clamp and said stamps are connected to saidmultiple actuators by means of transmission bars provided withT-connections at each end.
 3. A multiple-action furnace press accordingto claim 1, wherein said lower soleplate is provided, at each end, withcylindrical pillars for vertically guiding pivots disposed at the endsof said blade element, and with pillars for guiding said holding clamp.4. A multiple-action furnace press according to claim 1, wherein saidholding clamp includes cells for the passage and guidance of saidstamps, and a wall between said cells for longitudinally holding saidblade element and ensuring, during operation, holding of the centralpart throughout the length of the blade element to ensure clamping ofthe central fibre.
 5. A multiple-action furnace press for the hotforming of an element for use in the manufacture of a hollowturbomachine blade, comprising: a heating enclosure; a heater associatedwith said heating enclosure; a press structure surrounding said heatingenclosure and comprising a lower metal plate, an upper metal plate, andcolumns interconnecting said lower metal plate and said upper metalplate, said columns comprising prestressed tie rods; forming equipmentcomprising a lower soleplate incorporating a shaping die bounded at eachend by a respective notch, an upper holding clamp for holding saidelement on said shaping die during deformation, and at least two upperstamps; multiple actuators connected to said holding clamp and saidstamps; and a power unit for driving said multiple actuators.
 6. Amultiple-action furnace press according to claim 5, wherein said holdingclamp and said stamps are connected to said multiple actuators by meansof transmission bars provided with T-connections at each end.
 7. Amultiple-action furnace press according to claim 5, wherein said lowersoleplate is provided, at each end, with cylindrical pillars forvertically guiding pivots disposed at the ends of said blade element,and with pillars for guiding said holding clamp.
 8. A multiple-actionfurnace press according to claim 5, wherein said holding clamp includescells for the passage and guidance of said stamps, and a wall betweensaid cells for longitudinally holding said blade element and ensuring,during operation, holding of a central part throughout a length of theblade element to ensure clamping of a central fibre.